1. Field of the Invention
This invention relates to an impact tool for cutting a cable, more particularly to an automatic cable-cutting apparatus, which can be activated by operating a switch.
2. Description of the Related Art
Referring to FIG. 1, a cable holder 1 is shown to include several cable holding rows 11, each of which is provided with two elongated planar surfaces 12 that are located on two sides thereof. Each of the rows 11 includes a plurality of cable clamping units 14, each of which can hold a cable 13 thereon. Accordingly, thousands of cables 13 (only one is shown) can be fastened to the holder 1. When the cables 13 have been mounted on the holder 1, surplus lengths of the former are cut off by means of a blade 28 so as to prevent hindrance to subsequent mounting and checking of the cables 13.
Referring to FIG. 2, the blade 28 is disposed on a cable-cutting apparatus 2, which includes a housing 21, a cutter rod 22, a driving unit 23, a guiding ring 24, an impact rod 25, a large spring 26, and a force-adjusting unit 27. The cutter 22 is disposed slidably in the housing 21. The blade 28 is fixed to an end of the cutter rod 22. The driving unit 23 is disposed between the cutter rod 22 and the impact rod 25, and includes a driving member 231 and a coiled small spring 232, which has an inclined lowermost turn 2324 that presses against an outwardly extending lower end flange 233 of the driving member 231. As such, the axis of the driving member 231 is inclined. The driving member 231 has a large-diameter lower portion 234, on which the small spring 232 is sleeved fixedly, a truncated conical middle portion 235, and a small-diameter upper portion 236. The impact rod 25 is biased by the large spring 26 to press the guiding ring 24 against an inwardly extending flange 210 of the housing 21. The force-adjusting unit 27 includes a follower piece 271 and a rotary knob 272, which is formed integrally with an outwardly extending flange 273 that is received rotatably within an annular groove 211 in the housing 21. When the rotary knob 272 is rotated, a cam surface 274 of the rotary knob 272 pushes the follower piece 271 to further compress the large spring 26, thereby increasing the biasing force of the large spring 26.
Referring to FIG. 3, when a force is applied to the blade 28 so as to press a cable 13 against one of the planar surfaces 12, a top surface of the cutter rod 22 pushes the driving member 231 to move upward through a central hole 241 in the guiding ring 24. When the driving member 231 moves upward to contact the impact rod 25, it turns to a somewhat inclined position, where the small-diameter upper portion 236 is still somewhat deflected from a blind hole 251 in the central portion of a bottom end surface of the impact rod 25, as illustrated. Upon further application of a depressing force to the apparatus 2, the small-diameter upper portion 236 turns to register with the hole 251 in the impact rod 25, thereby permitting a rapid downward movement of the impact rod 25 relative to the driving member 231. Hence, the impact rod 25 can impact on the driving member 231 so as to cut the cable 13 with the blade 28. Although the aforementioned apparatus 2 can cut effectively the cable 13, the force needed to be exerted by a person to press the apparatus 2 against the cable 13 is too large to cut numerous cables 13 efficiently.
An object of this invention is to provide an automatic cable-cutting apparatus, which can be activated by operating a switch.
According to this invention, a cable-cutting apparatus includes a housing, a cutter rod with a fixed blade, an impact rod, a resilient unit for biasing the impact rod to press against the cutter rod, a rotating unit, and a driving unit. Normally, an engagement surface of the impact rod abuts against an engagement surface of the cutter rod. When the blade presses a cable against a planar surface, and when a switch of the driving unit is actuated to rotate the rotating unit, the engagement surface of the impact rod moves rearward away from the engagement surface of the cutter rod against the biasing action of the spring until the push rod reaches a rear limit position, after which the impact rod is biased by the spring to move forward to impact on the cutter rod, thereby cutting the cable with the blade.